Stevioside is a high-potency diterpenoid glycoside sweetener having the chemical structure:
Stevioside is isolated and extracted, along with other steviol glycosides, from the Stevia rebaudiana (Bertoni) plant (“Stevia”), which is commercially cultivated in Japan, Singapore, Taiwan, Malaysia, South Korea, China, Israel, India, Brazil, Australia, and Paraguay. It is an alternative non-caloric sweetener with functional and sensory properties superior to those of many high-potency sweeteners. Processed forms of Stevia can be 70 to 400 times more potent than sugar. The use of stevioside, however, is made more difficult by its low water solubility of approximately 1.25 g/L at room temperature (U.S. Pat. No. 4,082,858). Accordingly, it would be desirable to develop polymorphic and amorphous forms of stevioside that have improved rates of dissolution.
U.S. Pat. No. 5,962,678 discloses the re-crystallization of stevioside using an anhydrous methanol solution to obtain an 91.6% pure stevioside. By repeating the re-crystallization with aqueous methanol numerous times, the purity of stevioside may be increased to over 99%. U.S. Patent Publication No. 2007/0082103 discloses a method for purifying stevioside by recrystallization from methanol and then with 90% ethanol, asserting a two-step recrystallization from crude stevioside (64.6%) results in the formation of >99% pure stevioside in very high yield. These prior art methods, however, do not provide a substantially pure stevioside composition using only a single recrystallization step. Accordingly, it would be desirable to develop a method of purifying stevioside using a simple and economical crystallization method.